As disclosed in Applied Physics Letter 52(20), May 16, 1988, pp. 1724-1725, one of conventional Nb.sub.3 Al superconducting wires has been made by cold drawing a composite consisting of a Nb matrix and a large number of Al-alloy cores into a wire having ultrafine multicores and then heat-treating the cold drawn wire at a temperature ranging from 750.degree. to 950.degree. C. to form a Nb.sub.3 Al multifilamentary wire (refer to Composite Forming Process).
Japanese Laid Open Patent Publication No. 29017/87 discloses a Nb.sub.3 Al superconducting wire made by mixing Nb and Al powders, forming the mixture into a wire, irradiating an electron beam to the formed wire, and heat treating the irradiated wire at a temperature ranging from 500.degree. to 1000 .degree. C. to provide a final Nb.sub.3 Al superconducting wire (refer to Electron Beam Irradiation Process).
The composite forming process described above has several disadvantages, i.e. a stabilizing metal such as Cu or Al can not be compounded with a matrix; a stoichiometric composition of Nb.sub.3 Al cannot be obtained unless an ultrafine filament less than 1 .mu.m in diameter is formed; the Nb.sub.3 Al multifilamentary wire thus produced has a relatively low critical temperature and a critical magnetic field; and the critical current density falls is steeply at a high level of magnetic field such as 20 tesla.
The electron beam irradiation process described above can not, provide a Nb.sub.3 Al superconducting wire having an electromagnetically stable multifilamentary wire structure.